Mm In Phantom Research Articles

A Safe Framework for Quantitative In Vivo Human Evaluation of Image Guidance.

Goal: We present a new framework for in vivo image guidance evaluation and provide a case study on robotic partial nephrectomy. Methods: This framework (called the "bystander protocol") involves two surgeons, one who solely performs the therapeutic process without image guidance, and another who solely periodically collects data to evaluate image guidance. This isolates the evaluation from the therapy, so that in-development image guidance systems can be tested without risk of negatively impacting the standard of care. We provide a case study applying this protocol in clinical cases during robotic partial nephrectomy surgery. Results: The bystander protocol was performed successfully in 6 patient cases. We find average lesion centroid localization error with our IGS system to be 6.5 mm in vivo compared to our prior result of 3.0 mm in phantoms. Conclusions: The bystander protocol is a safe, effective method for testing in-development image guidance systems in human subjects.

Generating Patient-Specific Acoustic Simulations for Transcranial Focused Ultrasound Procedures Based on Optical Tracking Information.

Optical tracking is a real-time transducer positioning method for transcranial focused ultrasound (tFUS) procedures, but the predicted focus from optical tracking typically does not incorporate subject-specific skull information. Acoustic simulations can estimate the pressure field when propagating through the cranium but rely on accurately replicating the positioning of the transducer and skull in a simulated space. Here, we develop and characterize the accuracy of a workflow that creates simulation grids based on optical tracking information in a neuronavigated phantom with and without transmission through an ex vivo skull cap. The software pipeline could replicate the geometry of the tFUS procedure within the limits of the optical tracking system (transcranial target registration error (TRE): 3.9 ± 0.7 mm). The simulated focus and the free-field focus predicted by optical tracking had low Euclidean distance errors of 0.5±0.1 and 1.2±0.4 mm for phantom and skull cap, respectively, and some skull-specific effects were captured by the simulation. However, the TRE of simulation informed by optical tracking was 4.6±0.2, which is as large or greater than the focal spot size used by many tFUS systems. By updating the position of the transducer using the original TRE offset, we reduced the simulated TRE to 1.1 ± 0.4 mm. Our study describes a software pipeline for treatment planning, evaluates its accuracy, and demonstrates an approach using MR-acoustic radiation force imaging as a method to improve dosimetry. Overall, our software pipeline helps estimate acoustic exposure, and our study highlights the need for image feedback to increase the accuracy of tFUS dosimetry.

Augmented reality calibration using feature triangulation iteration-based registration for surgical navigation

BackgroundMarker-based augmented reality (AR) calibration methods for surgical navigation often require a second computed tomography scan of the patient, and their clinical application is limited due to high manufacturing costs and low accuracy. MethodsThis work introduces a novel type of AR calibration framework that combines a Microsoft HoloLens device with a single camera registration module for surgical navigation. A camera is used to gather multi-view images of a patient for reconstruction in this framework. A shape feature matching-based search method is proposed to adjust the size of the reconstructed model. The double clustering-based 3D point cloud segmentation method and 3D line segment detection method are also proposed to extract the corner points of the image marker. The corner points are the registration data of the image marker. A feature triangulation iteration-based registration method is proposed to quickly and accurately calibrate the pose relationship between the image marker and the patient in the virtual and real space. The patient model after registration is wirelessly transmitted to the HoloLens device to display the AR scene. ResultsThe proposed approach was used to conduct accuracy verification experiments on the phantoms and volunteers, which were compared with six advanced AR calibration methods. The proposed method obtained average fusion errors of 0.70 ± 0.16 and 0.91 ± 0.13 mm in phantom and volunteer experiments, respectively. The fusion accuracy of the proposed method is the highest among all comparison methods. A volunteer liver puncture clinical simulation experiment was also conducted to show the clinical feasibility. ConclusionsOur experiments proved the effectiveness of the proposed AR calibration method, and revealed a considerable potential for improving surgical performance.

A hybrid registration method using the mandibular bone surface for electromagnetic navigation in mandibular surgery.

To utilize navigated mandibular (reconstructive) surgery, accurate registration of the preoperative CT scan with the actual patient in the operating room (OR) is required. In this phantom study, the feasibility of a noninvasive hybrid registration method is assessed. This method consists of a point registration with anatomic landmarks for initialization and a surface registration using the bare mandibular bone surface for optimization. Three mandible phantoms with reference notches on two osteotomy planes were 3D printed. An electromagnetic tracking system in combination with 3D Slicer software was used for navigation. Different configurations, i.e., different surface point areas and number and configuration of surface points, were tested with a dentate phantom (A) in a metal-free environment. To simulate the intraoperative environment and different anatomies, the registration procedure was also performed with an OR bed using the dentate phantom and two (partially) edentulous phantoms with atypical anatomy (B and C). The accuracy of the registration was calculated using the notches on the osteotomy planes and was expressed as the target registration error (TRE). TRE values of less than 2.0mm were considered as clinically acceptable. In all experiments, the mean TRE was less than 2.0mm. No differences were found using different surface point areas or number or configurations of surface points. Registration accuracy in the simulated intraoperative setting was-mean (SD)-0.96 (0.22), 0.93 (0.26), and 1.50 (0.28) mm for phantom A, phantom B, and phantom C. Hybrid registration is a noninvasive method that requires only a small area of the bare mandibular bone surface to obtain high accuracy in phantom setting. Future studies should test this method in clinical setting during actual surgery.

Robustness Assessment of Images From a 0.35T Scanner of an Integrated MRI-Linac: Characterization of Radiomics Features in Phantom and Patient Data.

Purpose: Radiomics entails the extraction of quantitative imaging biomarkers (or radiomics features) hypothesized to provide additional pathophysiological and/or clinical information compared to qualitative visual observation and interpretation. This retrospective study explores the variability of radiomics features extracted from images acquired with the 0.35 T scanner of an integrated MRI-Linac. We hypothesized we would be able to identify features with high repeatability and reproducibility over various imaging conditions using phantom and patient imaging studies. We also compared findings from the literature relevant to our results. Methods: Eleven scans of a Magphan® RT phantom over 13 months and 11 scans of a ViewRay Daily QA phantom over 11 days constituted the phantom data. Patient datasets included 50 images from ten anonymized stereotactic body radiation therapy (SBRT) pancreatic cancer patients (50 Gy in 5 fractions). A True Fast Imaging with Steady-State Free Precession (TRUFI) pulse sequence was selected, using a voxel resolution of 1.5 mm × 1.5 mm × 1.5 mm and 1.5 mm × 1.5 mm × 3.0 mm for phantom and patient data, respectively. A total of 1087 shape-based, first, second, and higher order features were extracted followed by robustness analysis. Robustness was assessed with the Coefficient of Variation (CoV < 5%). Results: We identified 130 robust features across the datasets. Robust features were found within each category, except for 2 second-order sub-groups, namely, Gray Level Size Zone Matrix (GLSZM) and Neighborhood Gray Tone Difference Matrix (NGTDM). Additionally, several robust features agreed with findings from other stability assessments or predictive performance studies in the literature. Conclusion: We verified the stability of the 0.35 T scanner of an integrated MRI-Linac for longitudinal radiomics phantom studies and identified robust features over various imaging conditions. We conclude that phantom measurements can be used to identify robust radiomics features. More stability assessment research is warranted.

Image Guided Navigation Utilizing Intra-operative 3D Surface Scanning to Mitigate Morphological Deformation of Surface Anatomy

The purpose of this study is to navigate an in-house robot under uncertain intraoperative changes of the body surface which is not present in the pre-operative scan in hospital environments and lab environment. The proposed methodology involves the use of a 3D scanner to form a 3D model. The method used in this study is cost effective and takes less time (about 5–7 min). We focused more on the surface anatomical positions of a patient, which may change after a pre-operative scan. With respect to this, we introduced a method to include these deformed regions in navigation, which are not present in pre-operative scans. By creating an on-spot 3D surface model of the cadaver’s and phantom’s head, and after registration processes we completed the surgical navigation process with an error (root-mean-square error) of 0.568 mm and 0.791 mm for phantom and cadaver respectively. We showed the successful surgical navigation by using on-spot 3D surface modeling and including the deformity in our system. The accuracy of registration in lab condition and hospital condition was compared.

Next-generation frequency domain diffuse optical imaging systems using silicon photomultipliers

Diffuse optical imaging of biological tissue is a well-established methodology used to measure functional information from intrinsic contrast due to hemoglobin, water, and lipid. This information is exploited in frequency domain diffuse optical spectroscopy (FD-DOS) systems, which have been used to investigate chemotherapy response, optical mammography, and brain imaging. FD-DOS depth sensitivity and dynamic range are typically constrained by photodetector sensitivity. Here we present FD-DOS utilizing a silicon photomultiplier (SiPM) detector that has a higher signal-to-noise ratio (SNR) compared to an avalanche photodiode (APD), and thus enables extended source-detector (S/D) separations and increased depth penetration. We find the SiPM to have 10-30dB greater SNR than a comparably sized APD while detecting 1.5-2 orders of magnitude lower light levels, down to ∼4 pW at 50MHz modulation. The SiPM and APD recover optical property values of tissue-simulating phantoms within 13% agreement and are stable with 1% coefficient of variation over one hour. Finally, the SiPM is used to accurately recover optical properties in a reflectance geometry at S/D separations up to 48mm in phantoms mimicking human breast tissue.

P232] Deformable image registration for CT-images of the thorax region

Purpose Evaluate the performance of three commercial deformable image registration (DIR) algorithms for computed tomography (CT) images of the thorax. Methods Deformable registrations were performed on CT-images of a thorax phantom with tumor inserts and on six 4-dimensional patient CT-series of the thorax. For each DIR the shape and position of the deformed structures and the corresponding structures in the target image that the DIRs were set to reproduce, were compared for shifts between 0–53 mm. Two quantitative measures were used, the center of mass shift (CMS) and the Dice Similarity Coefficient (DSC) as well as visual examination of the registered images. Dose calculations on the deformed patient images were compared to calculations on the un-deformed target images for the gross tumor volume (GTV) (mean dose and D98%), lung (V20Gy, V12Gy), heart and spinal cord (D2%). Results In phantoms, moving structures with constant volume and shifts ⩽30 mm were reproduced with DSC⩾0.91 and CMS⩽0.9 mm by all the algorithms. For shifts >30 mm two algorithms failed. Deformations including volume changes were less accurate with 3/12 and 9/12 DIRs considered visually unacceptable, corresponding to CMS>2.0 mm and DSC Conclusions Visually acceptable DIRs were achievable for moving structures with constant volume and shifts ⩽30 mm in phantoms and shifts⩽16 mm in patients. Visually acceptable DIRs implied dose deviations ⩽3.6 percentage units on patient CT-images of the thorax region.

Flexible Microdisplacement Sensor for Wearable/ Implantable Biomedical Applications

Wireless monitoring systems are becoming a popular technology in noninvasive diagnosis. Based on current technological trends, low-power consumption, flexibility, small size, disposability, and low cost are the most important parameters to consider when designing sensors for biomedical applications. Echoing this trend, this paper presents a flexible wearable/implantable biocompatible sensor using wireless passive detection scheme, for future studying of the dynamics of an implanted abdominal mesh. Recording information about mechanical behavior of the implanted mesh helps in understanding hernia recurrence, among other post-surgical problems. Microfabricated sliding interdigitated gold plates and a circular coil (parallel inductor–capacitor tank) on a flexible substrate constitute the sensor’s main core. The capacitance and, in consequence, the resonant frequency of the sensor will vary according to the sliding magnitude, because the overlapping area between the interdigitated plates changes on sliding. Thus, the monitored resonant frequency is the sensor response. Different thicknesses cyclo-olefin polymer was used as a dielectric layer. Phantom was used to the ex vivo characterization of tissue behavior. The capacitor was tested in a 0– $600~\mu \text{m}$ displacement’s range. The measured sensitivity was 0.04 and 0.85 pF/ $50~\mu \text{m}$ in simulated conditions, with a resolution of less than $1~\mu \text{m}$ . The maximum sensitivity in the frequency range was 410 kHz/ $50~\mu \text{m}$ . The frequency shift can be detected by an external readout coil up to 20 mm in air and 10 mm in phantom. The experimental results confirm the scalability of the sensor.

Data Packet Transmission Through Fat Tissue for Wireless IntraBody Networks

This paper explores high data rate microwave communication through fat tissue in order to address the wide bandwidth requirements of intrabody area networks. We have designed and carried out experiments on an IEEE 802.15.4-based WBAN prototype by measuring the performance of the fat tissue channel in terms of data packet reception with respect to tissue length and power transmission. This paper proposes and demonstrates a high data rate communication channel through fat tissue using phantom and ex-vivo environments. Here, we achieve a data packet reception of approximately 96% in both environments. The results also show that the received signal strength drops by ∼1 dBm per 10 mm in phantom and ∼2 dBm per 10 mm in ex-vivo . The phantom and ex-vivo experimentations validated our approach for high data rate communication through fat tissue for intrabody network applications. The proposed method opens up new opportunities for further research in fat channel communication. This study will contribute to the successful development of high bandwidth wireless intrabody networks that support high data rate implanted, ingested, injected, or worn devices.

Validation of an electron Monte Carlo dose calculation algorithm in the presence of heterogeneities using EGSnrc and radiochromic film measurements

The purpose of this study is to validate Eclipse's electron Monte Carlo algorithm (eMC) in heterogeneous phantoms using radiochromic films and EGSnrc as a reference Monte Carlo algorithm. Four heterogeneous phantoms are used in this study. Radiochromic films are inserted in these phantoms, including in heterogeneous media, and the measured relative dose distributions are compared to eMC calculations. Phantoms A, B, and C contain 1D heterogeneities, built with layers of lung‐ (phantom A) and bone‐ (phantoms B and C) equivalent materials sandwiched in Plastic Water. Phantom D is a thorax‐anthropomorphic phantom with 2D lung heterogeneities. Electron beams of 6, 9, 12 and 18 MeV from a Varian Clinac 2100 are delivered to these phantoms with a 10×10 cm2 applicator. Monte Carlo simulations with an independent algorithm (EGSnrc) are also used as a reference tool for two purposes: (1) as a second validation of the eMC dose calculations, and (2) to calculate the stopping power ratio between radiochromic films and bone medium, when dose is measured inside the heterogeneity. Percent depth dose (PDD) film measurements and eMC calculations agree within 2% or 3 mm for phantom A, and within 3% or 3 mm for phantoms B and C for almost all beam energies. One exception is observed with phantom B and the 6 MeV, where measured PDDs and those calculated with eMC differ by up to 4 mm. Gamma analysis of the measured and calculated 2D dose distributions in phantom D agree with criteria of 3%, 3 mm for 9, 12, and 18 MeV beams, and criteria of 5%, 3 mm for the 6 MeV beam. Dose calculations in heterogeneous media with eMC agree within 3% or 3 mm with radiochromic film measurements. Six (6) MeV beams are not modeled as accurately as other beam energies. The eMC algorithm is suitable for clinical dose calculations involving lung and bone.PACS numbers: 87.10.Rt, 87.55.km

938 NEEDLE STEERING SYSTEM USING DUTY-CYCLED ROTATION FOR PERCUTANEOUS KIDNEY ACCESS

You have accessJournal of UrologyTechnology & Instruments: Robotics/Laparoscopy1 Apr 2011938 NEEDLE STEERING SYSTEM USING DUTY-CYCLED ROTATION FOR PERCUTANEOUS KIDNEY ACCESS Khaled Shahrour, Michael Ost, Nathan Wood, Stephen Jackman, Timothy Averch, and Cameron Riviere Khaled ShahrourKhaled Shahrour Pittsburgh, PA More articles by this author , Michael OstMichael Ost Pittsburgh, PA More articles by this author , Nathan WoodNathan Wood Pittsburgh, PA More articles by this author , Stephen JackmanStephen Jackman Pittsburgh, PA More articles by this author , Timothy AverchTimothy Averch Pittsburgh, PA More articles by this author , and Cameron RiviereCameron Riviere Pittsburgh, PA More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2011.02.856AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES A novel technique of percutaneous renal access (PRA) is needed to overcome the drawbacks of using rigid needles. If a flexible needle with a beveled tip is inserted into tissue, it will bend in the direction of the tip. The curve depends on the needle flexibility and tissue resistance. If the needle spins constantly during insertion, it follows a straight path as the bevel is negated. Alternating periods of spinning and stopping (duty-cycling) allows for proportional control of the trajectory in order to steer the needle in tissue non-traumatically. Our objective is to test the ability of the duty-cycled steerable needle system to follow a specific trajectory in vitro using phantom and swine kidneys. METHODS The nitinol needle has a 0.52mm diameter with a 7° bevel and is attached to a motor for inserting motion and to another motor for spinning. The system is controlled using a graphical user interface to automatically select tip orientation, insertion and spinning speeds based on the actual needle position. A PRA phantom kidney training model was used in which the minor calyces were set as target points and needle is followed in real-time by a camera. In swine experiments, needle is followed fluoroscopically into the contrast-filled calyces. The distance between the actual path of the needle and the planned path (cross track error) and the final needle position were the objective and subjective outcomes respectively. RESULTS The needle successfully entered the phantom and swine kidneys during all attempts. Mean cross track error was 0.71mm with a range between 0.05mm and 1.4mm in phantoms. In swine kidneys, the mean cross track error was 1.38 mm. CONCLUSIONS Duty-cycled needle can be successfully steered along a pre-planed path in vitro and in swine kidney. Further studies on cadaveric and live animals are warranted prior to clinical investigation. © 2011 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 185Issue 4SApril 2011Page: e376 Advertisement Copyright & Permissions© 2011 by American Urological Association Education and Research, Inc.MetricsAuthor Information Khaled Shahrour Pittsburgh, PA More articles by this author Michael Ost Pittsburgh, PA More articles by this author Nathan Wood Pittsburgh, PA More articles by this author Stephen Jackman Pittsburgh, PA More articles by this author Timothy Averch Pittsburgh, PA More articles by this author Cameron Riviere Pittsburgh, PA More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

SU‐GG‐T‐384: Validation of an Electron Monte Carlo Dose Calculation Algorithm in the Presence of Heterogeneities Using Radiochromic Film

Purpose: To validate electron beam dose distributions calculated with the electron Monte Carlo (eMC) algorithm in situations of bone and lung heterogeneities using radiochromic films. Method and Materials: Four heterogeneous phantoms are used in this study. Radiochromic films are inserted in these phantoms, including in heterogeneous media, and the measured relative dose distributions are compared to eMC calculations. Phantoms A, B and C contain 1D heterogeneities, built with layers of lung and bone equivalent materials sandwiched in Plastic Water. Phantom A has 1.5 cm of Plastic Water, 9 cm of lung material, and 5 cm of Plastic Water. Phantom B has 1 cm of Plastic Water, 1 cm of bone material, and 5 cm of Plastic Water. Phantom C is similar to phantom B but has 2 cm of bone material. Phantom D is a thorax anthropomorphic phantom with 2D lung heterogeneities. Electron beams of 6, 9, 12 and 18 MeV are delivered to these phantoms with a 10×10 cm2 applicator. Results: Percent depth dose (PDD) film measurements and eMC calculations agree within 2% or 3 mm for phantom A, and within 3% or 3 mm for phantoms B and C for almost all beam energies. One exception is observed with phantom B and the 6 MeV, where measured and calculated PDDs differ by up to 4 mm. Gamma analysis of the measured and calculated 2D dose distributions in phantom D agree with criteria of [3%, 3 mm] for 9, 12 and 18 MeV beams, and [5%, 3 mm] for the 6 MeV beam. Conclusion: Dose calculations in heterogeneous media with eMC agree within 3% or 3 mm with radiochromic film measurements. 6 MeV beams are not modeled as accurately as other beam energies. The eMC algorithm is suitable for clinical dose calculations involving lung and bone heterogeneous media.

Marker-free lung tumor trajectory estimation from a cone beam CT sinogram

An algorithm was developed to estimate the 3D lung tumor position using the projection data forming a cone beam CT sinogram and a template registration method. A pre-existing respiration-correlated CT image was used to generate templates of the target, which were then registered to the individual cone beam CT projections, and estimates of the target position were made for each projection. The registration search region was constrained based on knowledge of the mean tumor position during the cone beam CT scan acquisition. Several template registration algorithms were compared, including correlation coefficient and robust methods such as block correlation, robust correlation coefficient and robust gradient correlation. Robust registration metrics were found to be less sensitive to occlusions such as overlying tissue and the treatment couch. The mean accuracy of the position estimation was 1.4 mm in phantom with a robust registration algorithm. In two research subjects with peripheral tumors, the mean position and mean target excursion were estimated to within 2.0 mm compared to the results obtained with a ‘4D’ registration of 4D image volumes.

ExacTrac X-ray 6 degree-of-freedom image-guidance for intracranial non-invasive stereotactic radiotherapy: Comparison with kilo-voltage cone-beam CT

Background and purpose To compare the residual setup errors measured with ExacTrac X-ray 6 degree-of-freedom (6D) and cone-beam computed tomography (CBCT) for a head phantom and patients receiving intracranial non-invasive fractionated stereotactic radiotherapy (SRT). Materials and methods Setup data were collected on a Novalis Tx treatment unit for an anthropomorphic head phantom and 18 patients with intracranial tumors. Initial corrections were determined and corrected with the ExacTrac system only, and then the residual setup error was determined by means of three different procedures. These procedures included registrations of ExacTrac X-ray images with the corresponding digitally reconstructed radiographs (DRRs) using the ExacTrac 6D fusion, and registrations of CBCT images with the planning CT using both online 3D fusion and offline 6D fusion. The difference in residual setup errors between ExacTrac system and CBCT was computed. The impact of rotations on the difference was evaluated. Results A modest difference in residual setup errors was found between ExacTrac system and CBCT. The root-mean-square (RMS) of the differences observed for translations was typically <0.5 mm for phantom, and <1.5 mm for patients, respectively. The RMS of the differences for rotation(s) was however <0.2 degree for phantom, and <1.0 degree for patients, respectively. The impact of rotation on the setup difference was minor but not negligible. Conclusions This study indicates that there is a general agreement between ExacTrac system and CBCT.

Evaluation of radiograph-based interstitial implant dosimetry on computed tomography images using dose volume indices for head and neck cancer

Conventional radiograph-based implant dosimetry fails to correlate the spatial dose distribution on patient anatomy with lack in dosimetry quality. Though these limitations are overcome in computed tomography (CT)-based dosimetry, it requires an algorithm which can reconstruct catheters on the multi-planner CT images. In the absence of such algorithm, we proposed a technique in which the implanted geometry and dose distribution generated from orthogonal radiograph were mapped onto the CT data using coordinate transformation method.Radiograph-based implant dosimetry was generated for five head and neck cancer patients on Plato Sunrise treatment planning system. Dosimetry was geometrically optimized on volume, and dose was prescribed according to the natural prescription dose. The final dose distribution was retrospectively mapped onto the CT data set of the same patients using coordinate transformation method, which was verified in a phantom prior to patient study. Dosimetric outcomes were evaluated qualitatively by visualizing isodose distribution on CT images and quantitatively using the dose volume indices, which includes coverage index (CI), external volume index (EI), relative dose homogeneity index (HI), overdose volume index (OI) and conformal index (COIN).The accuracy of coordinate transformation was within ±1 mm in phantom and ±2 mm in patients. Qualitative evaluation of dosimetry on the CT images shows reasonably good coverage of target at the expense of excessive normal tissue irradiation. The mean (SD) values of CI, EI and HI were estimated to be 0.81 (0.039), 0.55 (0.174) and 0.65 (0.074) respectively. The maximum OI estimated was 0.06 (mean 0.04, SD = 0.015). Finally, the COIN computed for each patient ranged from 0.4 to 0.61 (mean 0.52, SD = 0.078).The proposed technique is feasible and accurate to implement even for the most complicated implant geometry. It allows the physicist and physician to evaluate the plan both qualitatively and quantitatively. Dose volume indices derived from CT data set are useful for evaluating the implant and comparing different brachytherapy plans. COIN index is an important tool to assess the target coverage and sparing of normal tissues in brachytherapy.

UTSW Small Animal Positron Emission Imager

A Small Animal Imager (SAI) for PET has been designed, built, tested in phantoms, and applied to investigations in mice and rats. The device uses principles based on gamma-ray induced scintillation in crossed fiber optic detectors connected to Position Sensitive Photomultiplier Tubes (PSPMT). Each detector consists of an epoxied stack of 28 layers of 135 round 1 mm BCF-10 scintillating plastic fibers. The overlap region forms a 13.5times13.5times2.8 cm3 detector volume. Scintillating light from the fibers is detected by two (X and Y directions) Hamamatsu R-2486 PSPMTs with 16 anode wires in each of two orthogonal directions. A centroid-finding algorithm gives the position of a light cluster on the face (photocathode) of a PSPMT. The accuracy of the reconstruction of an interaction position is essentially independent of light cluster position. This translates to a nearly isotropic photon response for the entire detector. The system has been used to test several 3D image reconstruction algorithms, software modifications, and improvements. The sensitivity (~12.6 cps/kBq at 9 cm inner diameter) and sub-millimeter spatial resolution (better than 1 mm in phantoms) obtained with an iterative algorithm incorporating system modeling make the SAI a relatively inexpensive high performance animal imager. The SAI is currently being used for imaging experiments in mice and rats

A spin-spin relaxation rate investigation of the gelatin ferrous sulphate NMR dosimeter

Spin-spin NMR relaxation rate in the ferrous sulphate gelatin dosimeter has been studied in terms of pH, gelatin concentration, the addition of benzoic acid, and sample size. It is demonstrated that R2 is more sensitive to changes in Fe3+ ion concentration than R1 when measuring at frequencies of 64 and 100 MHz. pH has an important effect on dose response curves, and oxygen depletion occurs significantly more rapidly in FeSO4 gelatin than in the liquid FeSO4, resulting in a saturation dose of approximately 80 Gy at depths greater than approximately 3 mm in phantom. The concentration of gelatin can be increased to 12% by weight, and the dosimeter will continue to exhibit a linear dose response. Sensitivity is maintained at higher gel concentrations by pH compensation. Addition of low-concentration benzoic acid to the system does not alter the dose response of the gelatin FeSO4 system. Finally, spontaneous oxidation of Fe2+ ions does not significantly alter the shape of dose response curves but does result in increases in R2 by up to 4% per day.